In the manufacture of electrical motors, the more magnet wire which can be inserted into a stator core, the more efficient the motor performance. In addition to motor efficiency considerations, motor manufacturers are also interested in manufacture efficiency. Accordingly, such coils where possible are inserted automatically, generally by two methods: either a gun-winding method or a slot insertion method. In the older gun-winding method, the winding is done by carrying the wire into the stator slot by means of a hollow winding needle. Turns are made by the circular path of the gun to accommodate the individual coil slots. As described in Cal Towne's paper entitled "Motor Winding Insertion" presented at the Electrical/Electronics Insulation Conference, Boston, Massachusetts in September, 1979, in the more preferred slot insertion method, coils are first wound on a form, placed on a transfer tool and then pressed off the transfer tool into the stator core slots through insertion guides or blades. In order to accommodate these automated insertion methods, wire manufacturers have responded by producing magnet wires with insulating coatings with low coefficients of friction. Note, for example, U.S. Pat. Nos. 3,413,148; 3,446,660; 3,632,440; 3,775,175; 3,856,566; 4,002,797; 4,216,263; and Published European Patent Application No. 0-033-244, published Aug. 5, 1981 (Bulletin 8/31).
With the availability of such low friction insulating coatings motor manufacturers began to take advantage of such coatings by inserting an increasing number of wires per slot into the motors. However, it was also well known in this art that there existed a locking wire size range where based on the size of the insulated wires themselves, attempts at inserting a certain number of wires into a particular size slot opening at one time caused a wedging action of the wires with resulting damage to the coated wires. In spite of this fact, in the interest of efficiency and a better product, motor manufacturers continue to insert in a range closely approaching the locking wire size range even though discouraged from doing so by power insertion equipment manufacturers. And while nylon overcoated wires have been known to be successfully inserted in a locking wire size range, polyamide-imide overcoated wires, although making superior magnet wire products (e.g. in water resistance and temperature stability) have not been successfully power inserted in the locking wire size range.
Accordingly, what is needed in this art, is an insulated magnet wire having a polyamide-imide insulation coating which can be power inserted into a coil slot in the locking wire size range without damage to the wire.